Compressor rotor blade undercut

ABSTRACT

A rotor blade for an axial compressor that may include an airfoil, which includes a leading edge, and a root, which includes a platform, the platform being the outer radial face of the root from which the airfoil extends, and a dovetail, the dovetail including a dovetail leading-face, which is the face of the dovetail that generally points up-stream once the rotor blade is installed in the axial compressor. The rotor blade may include an undercut groove that is formed on the dovetail leading-face that undercuts at least partially the intersection of the leading edge of the airfoil and the platform.

BACKGROUND OF THE INVENTION

This present application relates generally to compressor blades in turbine engines. More specifically, but not by way of limitation, the present application relates to compressor rotor blades that are designed and configured to reduce operational stresses to certain areas of the blade such that the blade is more resistant to erosion.

In a gas turbine engine, the compressor generally includes multiple stages that have a row of rotor blades (also commonly referred to as “rotor airfoils” or “compressor blades”) and stator blades (also commonly referred to as “stator airfoils”). The rotor blades rotate about a rotor and, thusly, impart kinetic energy to the airflow through the compressor. Directly following the row of rotor blades is a row of stator blades, which remain stationary. Acting in concert, the rotor blades and stator blades turn the airflow and slow the air velocity, respectively, which increases the static pressure of the airflow through the compressor. Usually multiple stages of rotor blades and stator blades are stacked in an axial flow compressor to achieve the required discharge to inlet air pressure ratio. Rotor and stator blades generally are secured to rotor wheels and the stator case, respectively, by means of a dovetail or root or base attachment.

To improve compressor performance, a water wash is preformed periodically to clean the rotor and stator blades. During this process, water is sprayed directly into the inlet of an operating compressor. The water impacts the first stage rotor blade, and then is carried along with the flow of air through the compressor such that the remaining rotor and stator blades are also cleaned. The impact of the water on the rotor blades, particularly the leading edges of the rotor blades in the first stage, causes erosion. This erosion generally results in the formation of small pits and/or crevices along the leading edge of the rotor blades. As this process is repeated, the pits and crevices deepen and widen.

As one of ordinary skill in the art will appreciate, rotor blades are subject to high levels of mechanical stresses during operation because of the rotational velocity of the compressor. This high level of stress affects the rate at which the erosion on the leading edges of the rotor blades occurs. That is, the amount of erosion experienced by the leading edge of the rotor blades is generally proportional to the level of stress being experienced at that location. As the stress increases, so does the rate of erosion. Over time, the high stress levels and the accrued erosion can lead to a high cycle fatigue crack in the rotor blade, which ultimately can lead to blade failure. Of course, a rotor blade failure that occurs during operation can lead to catastrophic damage to the downstream components of the turbine. As a result, there is a continuing need for improved systems, methods and apparatus that better protect against this possibility. More particularly, there is a need for improved rotor blades that function with reduced stress levels at the leading edge such that the blades are more erosion resistant.

BRIEF DESCRIPTION OF THE INVENTION

The present application thus describes a rotor blade for an axial compressor that may include an airfoil, which includes a leading edge, and a root, which includes a platform, the platform being the outer radial face of the root from which the airfoil extends, and a dovetail, the dovetail including a dovetail leading-face, which is the face of the dovetail that generally points up-stream once the rotor blade is installed in the axial compressor. The rotor blade may include an undercut groove that is formed on the dovetail leading-face that undercuts at least partially the intersection of the leading edge of the airfoil and the platform.

The present application further describes a rotor blade for an axial compressor that may include an airfoil and a root. The airfoil may include an airfoil suction-side, an airfoil pressure-side, and a leading edge, which is the edge defined between the airfoil suction-side and the airfoil pressure-side that generally points up-stream once the rotor blade is installed in the axial compressor. The root may include a platform, which is the outer radial face of the root from which the airfoil extends, and a dovetail that is used to connect the rotor blade to a rotor wheel. The dovetail may include a dovetail leading-face, which is the face of the dovetail that generally points up-stream once the rotor blade is installed in the axial compressor, a dovetail suction-side and a dovetail pressure-side. The rotor blade also may include an undercut groove that is formed on the dovetail leading-face that substantially undercuts the intersection of the leading edge of the airfoil and the platform. The undercut groove may begin in the approximate center of the dovetail leading-face and extends toward an edge of the dovetail that separates the dovetail leading-face and the dovetail pressure side.

These and other features of the present application will become apparent upon review of the following detailed description of the preferred embodiments when taken in conjunction with the drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of this invention will be more completely understood and appreciated by careful study of the following more detailed description of exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of a typical compressor rotor blade.

FIG. 2 is a perspective view of a compressor rotor blade illustrating an undercut groove according to an exemplary embodiment of the present application.

FIG. 3 is a perspective view of a compressor rotor blade illustrating an undercut groove according to an alternative embodiment of the present application.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures, where the various numbers represent like parts throughout the several views, FIG. 1 demonstrates a conventional rotor blade 10. As one of ordinary skill in the art will appreciate, the rotor blade 10 may include an airfoil 12, which, when spun about the rotor, imparts kinetic energy to air flowing through the compressor, and a base or root 13. The airfoil 12 generally includes a suction-side 14 (i.e., convex-side) and a pressure-side 16 (i.e., concave-side). The airfoil 12 further has a leading edge 17, which is the edge between the suction-side 14 and the pressure-side 16 that generally points up-stream once the rotor blade 10 is installed in the compressor.

The root 13 includes a platform 18, which is the outward radial face of the root 13 from which the airfoil 12 extends. The platform 18 may be integrally joined to the root 13 of the rotor blade 10. The platform 18 defines the radial inner boundary of the airflow across the airfoil 12. As one of ordinary skill in the art will appreciate, the root 13 further generally includes a dovetail 20 that connects via a complimentary groove in the rotor wheel (not shown) to secure the rotor blade 10 in the appropriate position within the compressor. The dovetail 20 may include a dovetail leading-face 22, which constitutes the leading-face of the dovetail 18, i.e., the face of the dovetail 18 that, once installed, generally points up-stream in the compressor. The dovetail 20 further may include a dovetail suction-side 24 (which is on the same side as the airfoil suction-side 14) and a dovetail pressure-side 26 (which is on the same side as the airfoil pressure-side 16).

In use, the dovetail 20 of the rotor blade 10 of FIG. 1 fits somewhat loosely in the corresponding compressor wheel slot until the rotor begins to rotate. As the wheel rotates, centrifugal force pushes the dovetail 20 firmly radially outward against the slot (or other retainment feature) in the compressor wheel. The reaction force is developed at the pressure face of the wheel, which counteracts the centrifugal forces created by the rotating blade 10. The centrifugal force creates stresses in the rotor blade 10. As one of ordinary skill in the art will appreciate, the stresses typically concentrate in the airfoil 12 at certain locations. One of the locations of concentrated stress is the inner radial portion of the leading edge 17 of the airfoil 12 (i.e., the leading edge 17 near where it connects to the platform 18). This location of concentrated stress will hereafter generally be referred to as the “base of the leading edge” or “leading edge base” (and noted on the FIGS. as 28). As described above, the high stresses during operation at the leading edge base 28 causes water erosion to degrade and weaken the rotor blade 10 more rapidly at this location. This degradation may negatively impact the useful life of the rotor blade 10.

In an exemplary embodiment of the present application, as seen in FIG. 2, a rotor blade 30, such as, for example, a rotor blade used in the axial compressor of an industrial gas turbine engine, generally includes an airfoil 12, with a suction-side 14 and a pressure-side 16, a root 13, with a platform 18 and a dovetail 20 (which includes a dovetail leading-face 22, a dovetail suction-side 24, and a dovetail pressure-side 26) that is used to connect the blade to the compressor wheel (not shown). Generally, the dovetail 20 attaches the rotor blade 10 to the rim of the wheel such that an array of rotor blades 10 is arranged around the perimeter of the wheel to form an annular row of blades 10.

FIG. 2 further illustrates an undercut groove 32 according to an exemplary embodiment of the present invention, which, in use, may advantageously reduce the stress experienced by the airfoil 12 at the leading edge base 28 (which, as described above, is the area of the leading edge 17 near where the leading edge 17 connects to the platform 18). The undercut groove 32 generally may include a groove formed in the dovetail leading-face 22 just radially inward of radial height of the platform 18 and approximately under (i.e., radially inward of) the intersection of the leading edge 17 and the platform 18. Note that the description of the location of the undercut groove 32 is meant to generally describe the location of the groove in relation to where the leading edge 17 connects to the platform 18, and also in relation to the dovetail leading-face 22, the dovetail pressure side 26, and the dovetail suction side 24. Under certain circumstances, the rotor blade structure elements identified in the preceding sentence may take a slightly different form and be referred to with alternative names (for example, when the manner in which the rotor blade 10 is connected to the wheel is different from the dovetail-slot arrangement described above). One of ordinary skill in the relevant art will readily appreciate that the present application may still be applicable to such rotor blades as long as the basic shape and relative location of the undercut groove 32 remains substantially similar. Thus, though specific names, such as “dovetail”, are used herein to describe certain features of the rotor blade 10, it is intended that these names not be limiting and that this application should remain applicable to rotor blades having substantially similar features.

In one or more embodiments of the present application, the undercut groove 32 may include the following characteristics, though each of these attributes may not be included in every embodiment. The undercut groove 32 generally is a groove that extends through the dovetail leading-face 22 into the dovetail 20 such that the intersection of the platform 18 and the leading edge 17 is undercut. Per the perspective and orientation of the rotor blade 10 in FIG. 2, undercut may be defined to mean that the undercut groove 32 extends into the dovetail 20 such that the volume of dovetail 20 beneath and in close proximity to the intersection of the platform 18 and the leading edge 17 is at least partially (and, in other embodiments, substantially or completely) removed. The location of the removed volume of dovetail 20 may also be described as a volume that is in close proximity to the platform 18 and more radially inward than the intersection of the platform 18 and the leading edge 17. That is, the undercut groove 32 extends to a depth in the dovetail so that it is axially aligned with at least a portion of the intersection of the platform 18 and the leading edge 17.

As illustrated, the undercut groove 32 may begin substantially in the approximate center of the dovetail leading-face 22 and extend toward the edge of the dovetail 20 that separates the dovetail leading-face 22 and the dovetail pressure side 26. As such, and as illustrated in FIG. 2, the undercut groove 32 may open through the dovetail pressure side 26.

The undercut groove 32 may form an approximate profile when viewed on the dovetail leading-face 22 and on the dovetail pressure-side 26. As illustrated in FIG. 2, on the dovetail leading-face 22, the profile may be substantially rectangular (note that one side of the rectangle is missing because of the fact that the undercut groove 32 extends through the edge of the dovetail 20 that separates the dovetail leading-face 22 and the dovetail pressure side 26). In some embodiments and as illustrated in FIG. 2, because of the fillet regions the corners and the opening through the dovetail pressure side 26, the rectangular shape may form an approximate “U” shape, though, when viewed from the perspective in FIG. 2, the “U” appears as if it has been rotated approximately 90 degrees counterclockwise. Note that in other embodiments, the angle of rotation, as it appears from the perspective in FIG. 2, may slightly larger or smaller than 90 degrees.

On the dovetail pressure-side 26, the profile also may be somewhat rectangular (note that, like above, one of the sides of the rectangle also is missing). Because of the fillet regions in the corners, the rectangular shape on the dovetail pressure-side 26 also may form an approximate “U” shape, though, in this case, when viewed from the perspective in FIG. 2, the “U” appears as if it is laying on its side, i.e., as if it has been rotated approximately 90 degrees clockwise. Note that in other embodiments, the angle of rotation, as it appears from the perspective in FIG. 2, may slightly larger or smaller than 90 degrees.

The undercut groove 32 may be formed such that the radially outward edge of the groove 32 is just below (or radially inward of) the platform 18. Generally, the distance between the radially outward edge of the undercut groove 32 and the platform will be approximately 0.1 to 1.0 inches, though measurements outside of this range are also possible. The radially outward edge of the undercut groove 32 may be oriented such that it is substantially parallel to the dovetail platform 18. In forming the undercut groove 32, the angle of the cut into the dovetail leading-face 22 and the size of the cut may be optimized. In some embodiments and as seen in FIG. 2, the angle of the cut into the dovetail leading-face 22 may be approximately 90 degrees with respect to a mean camber line of the airfoil 12 at the platform 18 section. In this manner, the loading on the undercut groove 32 in operation is generally distributed along the length of the groove.

The depth of the undercut groove 32 will affect the distance through which the operational stresses get relocated from the leading edge base 28 of the airfoil 12. Deeper grooves generally mean that the leading edge base 28 will experience lower stresses during operation. In some embodiments, the undercut groove 32 will have a depth such that the groove 32 enters a stress line of the compressor rotor blade at the leading edge base 18 caused by blade load during operation. That is, the depth of the undercut groove 32 will be such so that the area in the dovetail that is radially inward of the intersection of the platform 18 and the leading edge 17 is at least partially (and, in other embodiments, substantially or completely) removed.

In operation, the undercut groove 32 generally causes a change to the load path direction away from the leading edge 17. The groove reduces the stress developed at the leading edge 17 of the airfoil 12, especially at the leading edge base 28 where the airfoil 12 attaches the platform 18. In general, as one of ordinary skill in the art will appreciate, stress reduction occurs because the leading edge base 28 is essentially disconnected from the dovetail 20 directly. As described above, lowering the stress at the leading edge 17 and/or the leading edge base 28 generally means a reduction of erosion at these locations and a longer part life for the rotor blades 10. Further, the shape of the undercut groove 32 is relatively simple to manufacture.

As one of ordinary skill in the art will appreciate, it may be desirable to fill the undercut groove 32 with a plug (not shown) during operation. As illustrated in FIG. 3, the undercut groove 32, in an alternative embodiment, may have a shape that is conducive to retaining an inserted plug. In such an embodiment, the undercut groove 32 may taper such that the width of the undercut groove 32 is narrowed at the dovetail leading face 22 and wider as the undercut groove 32 extends into the dovetail 20. That is, the undercut groove 32 flares outwardly from the opening at the dovetail leading-face 22 such that the groove 32 becomes wider as it extends into the dovetail 20. With this configuration, a plug that is formed to fit relatively snugly in the undercut groove 32 will not be able to exit the undercut groove 32 from the dovetail leading-face 22 because the groove opening is too narrow. Such a plug, though, will be able to be conveniently inserted from the dovetail pressure-side 26. The plug may be made of any material that is able to withstand the harsh conditions within the compressor; for example, the plug may be made of nylon.

In some embodiments, the undercut groove 32 may be used in first stage rotor blades, where erosion often is most harsh. In other embodiments, the undercut groove 32 may be used in all stages of the compressor.

From the above description of preferred embodiments of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims. Further, it should be apparent that the foregoing relates only to the described embodiments of the present application and that numerous changes and modifications may be made herein without departing from the spirit and scope of the application as defined by the following claims and the equivalents thereof. 

1. A rotor blade for an axial compressor that comprises an airfoil, which includes a leading edge, and a root, which includes a platform, the platform being the outer radial face of the root from which the airfoil extends, and a dovetail, the dovetail including a dovetail leading-face, which is the face of the dovetail that generally points up-stream once the rotor blade is installed in the axial compressor, the rotor blade comprising: an undercut groove that is formed on the dovetail leading-face that undercuts at least partially the intersection of the leading edge of the airfoil and the platform.
 2. The rotor blade according to claim 1, wherein: the airfoil further includes an airfoil suction-side and an airfoil pressure-side; the leading edge of the airfoil is the edge defined between the airfoil suction-side and the airfoil pressure-side that generally points up-stream once the rotor blade is installed in the axial compressor; the dovetail is used, at least in part, to connect the rotor blade to a rotor wheel; and the dovetail further includes a dovetail suction-side and a dovetail pressure-side, each of which, respectively, correspond to the same side of the rotor blade as the airfoil suction-side and the airfoil pressure-side.
 3. The rotor blade according to claim 1, wherein the undercut groove substantially undercuts the intersection of the leading edge of the airfoil and the platform.
 4. The rotor blade according to claim 1, wherein the undercut groove completely undercuts the intersection of the leading edge of the airfoil and the platform.
 5. The rotor blade according to claim 1, wherein the phrase “undercuts at least partially the intersection of a leading edge of the airfoil and the platform” is defined to mean that the undercut groove extends to a depth in the dovetail such that a portion of the undercut groove is axially aligned with at least a portion of the intersection of the leading edge of the airfoil and the platform.
 6. The rotor blade according to claim 1, wherein the undercut groove is positioned such that it is in close proximity to and radially inward of the radial height of the platform.
 7. The rotor blade according to claim 6, wherein the distance between the outward most radial height of the undercut groove and the radial height of the platform is between approximately 0.1 to 1.0 inches.
 8. The rotor blade according to claim 6, wherein the undercut groove begins in the approximate center of the dovetail leading-face and extends toward an edge of the dovetail that separates the dovetail leading-face and the dovetail pressure side.
 9. The rotor blade according to claim 8, wherein the undercut groove extends through the dovetail pressure-side such that the undercut groove is open through the dovetail pressure-side.
 10. The rotor blade according to claim 9, wherein the undercut groove tapers such that the width of the undercut groove is narrower at the dovetail leading-face and wider as the undercut groove extends into the dovetail.
 11. The rotor blade according to claim 8, wherein the undercut groove is substantially parallel to the platform.
 12. The rotor blade according to claim 1, wherein the undercut groove comprises a substantially rectangular profile on the dovetail leading-face and on the dovetail pressure-side.
 13. The rotor blade according to claim 1, wherein the undercut groove comprises a substantially “U” shape profile on the dovetail leading-face and on the dovetail pressure-side.
 14. The rotor blade according to claim 1, wherein the angle of the cut into the dovetail leading-face that is made to form the undercut groove is approximately 90 degrees with respect to a mean camber line of the airfoil at the platform.
 15. The rotor blade according to claim 1, wherein the depth of the undercut groove is such to that the undercut groove enters the stress line of the rotor blade at a base of the leading edge that is caused by blade load during operation of the axial compressor.
 16. The rotor blade according to claim 1, wherein the rotor blade is configured to function in a first stage of the axial compressor.
 17. A rotor blade for an axial compressor that includes an airfoil and a root, the airfoil including an airfoil suction-side, an airfoil pressure-side, and a leading edge, which is the edge defined between the airfoil suction-side and the airfoil pressure-side that generally points up-stream once the rotor blade is installed in the axial compressor, the root including a platform, which is the outer radial face of the root from which the airfoil extends, and a dovetail that is used to connect the rotor blade to a rotor wheel, the dovetail including a dovetail leading-face, which is the face of the dovetail that generally points up-stream once the rotor blade is installed in the axial compressor, a dovetail suction-side and a dovetail pressure-side, the rotor blade comprising: an undercut groove that is formed on the dovetail leading-face that substantially undercuts the intersection of the leading edge of the airfoil and the platform; wherein the undercut groove begins in the approximate center of the dovetail leading-face and extends toward an edge of the dovetail that separates the dovetail leading-face and the dovetail pressure side.
 18. The rotor blade according to claim 17, wherein the undercut groove extends through the through the dovetail pressure-side such that the undercut groove is open through the dovetail pressure-side.
 19. The rotor blade according to claim 18, wherein: the distance between the outward most radial height of the undercut groove and the radial height of the platform is approximately 0.1 to 1.0 inches; and the undercut groove is substantially parallel to the platform.
 20. The rotor blade according to claim 17, wherein the angle of the cut into the dovetail leading-face is approximately 90 degrees with respect to a mean camber line of the airfoil at the platform. 